A propulsion system provided on a boat typically has an engine for obtaining a propulsion force by rotating a propeller using the power of the engine. Some boat propulsion systems have an engine control unit by which the fuel injection amount, the amount of air, or the ignition timing are controlled based on the engine speed, the intake pressure in the downstream side of the throttle valve, or the throttle position.
For example, according to the operating status control device for the internal combustion engine disclosed in Japanese Patent Document JP-A-Hei 06-117315, the control values for an engine operating status are determined based on the predicted value of the intake pressure. Specifically for this example, an intake pressure is detected by sampling, and a predicted value is obtained by multiplying the difference between the present detected value and the previously detected value by a prediction coefficient, with the present value then added to the value obtained by the multiplication. In such a computation of the predicted value, different prediction coefficients are applied to the acceleration state and to the deceleration state of the engine for determining a predicted intake pressure, based on which of the control values is determined for the applicable engine operating status.
As another example according to an abrupt acceleration and an abrupt deceleration control method and device for the internal combustion engine disclosed in Japanese Patent Document JP-A-Hei 09-004488, the fuel injection amount and the ignition timing are controlled in a manner such that the control method can catch up with the change in speed during an abrupt acceleration or deceleration to improve the acceleration performance and to prevent engine stall during the deceleration. Such a control method uses a correction table (map) containing the spark advance or spark retard angle and the additional fuel injection amount applicable to the abrupt acceleration, along with a correction table (map) containing the additional fuel injection amount applicable to the abrupt deceleration for controlling the engine with the increased fuel injection amount after the correction and the ignition timing after the adjustment.
As a further example according to other conventional engine control units for a boat propulsion system, a predicted boat speed value map based on the engine speed and the intake pressure is prepared, the engine speed and the intake pressure are detected, and a mapped value is extracted from the predicted boat speed value map in relation to the detected values, and the amount of air and the fuel injection amount are determined according to the mapped value. Specifically for this example, the boat speed was detected as a value determined by the mapped value extracted from the predicted boat speed value map based on the engine speed and the load. The predicted boat speed during the deceleration is determined by the computation utilizing the mapped value as an initial base value, because the amount of air and the fuel injection amount must be increased to prevent the engine stall in the course of deceleration.
In prior conventional approaches, not the mapped value but rather the tailing (a process of gradually dropping the boat speed first, and then recovering the speed gradually) was utilized for detecting the engine speed and the intake pressure. Also, the shift-in and shift-out operations involving the different loads were distinguished by detecting the neutral switch on and off operation, and after extracting the attenuation coefficient (attenuation time and attenuation amount) from the map, which is set to be different between the shift-in and shift-out operations, the predicted boat speed value was determined by applying the detected values of the rotational speed and the intake pressure, the attenuation coefficient, and the cycle. Then, the applicable amount of air and the fuel injection amount were determined according to the predicted boat speed value.
The boat speed during the deceleration was estimated by the predicted value obtained by attenuating the speed to the end of a time limit that was set to be different between the shift-in and shift-out operations. In addition, when the boat speed transitions from the deceleration to the non-deceleration state (namely, the constant speed or the acceleration), the speed was recovered by given increments toward the boat speed determined by the rotational speed and the intake pressure. Therefore, if the acceleration took place between the deceleration and the recovery from the deceleration, the predicted speed value may deviate from the actual boat speed, resulting in poor acceleration in the course of speed recovery from the deceleration.